How to tweak the radius scale of Sapling tree Gen add-on in blender v2.79?

I'm following a Youtube tutorial on how to create a tree. The person in the tutorial is using Blender v2.75 while I'm using v2.79. He decreased the tree's radius scale to make it look more realistic, but I cannot find the same thing in my toolbar. I played with the custom shape settings but none of them seems to be right. Googled and found nothing helpful for this. Does anyone know where to find it in v2.79? Thank you!